1. Field of the Invention
The present invention relates to a novel polycarbonate, more particularly, to a novel polycarbonate which is excellent in flame retardance, impact resistance, and thermostability at molding.
2. Description of the Related Arts
As halogen-containing polycarbonate copolymers having flame retardance, various ones have heretofore been known. They include (i) a copolymer of tetrabromobisphenol A (TBA) and bisphenol A (BPA) (Japanese Patent Publication No. 24660/1972), (ii) a copolymer of tetrabromobisphenolsulfone (TBS) and BPA (Japanese Patent Application Laid-Open No. 123294/1976), (iii) a copolymer of tetrabromothiobisphenol (TBTDP) and BPA (Japanese Patent Application Laid-Open No. 99226/1981), (iv) a copolymer of the statistical mixture of halogenated bisphenols and BPA (Japanese Patent Application No. 136796/1976), and (v) a blend of the copolymer of thiobisphenol (TDP) and BPA and the copolymer of above (i) (Japanese Patent Application Laid-Open No. 50065/1979).
These copolymers are obtained by copolymerization of halogenated bisphenols resulted from halogen-substitution of benzene nucleus in bisphenols for the purpose of containing halogen in an amount necessary for a sufficient flame retardance. All of these copolymerization, however, require these halogenated bisphenols in a comparatively large amount, and accordingly, the mechanical strength of the resulting polycarbonate (particularly, impact resistance) is lowered.
Another example of halogen-containing polycarbonate is a polycarbonate in which halogenated phenol is used as the end terminator (Japanese Patent Publication No. 40715/1971). Said polycarbonate, however, is not provided with both of an excellent flame-retardance and a high mechanical-strength.
In order to overcome above disadvantages, a polycarbonate was produced by a process of copolymerizing BPA, TBA and TDP (Japanese Patent Application Laid-Open No. 140597/1977). According to said process, the resulting polycarbonate is excellent in both of flame retardance and mechanical strength, but it is not improved so much in moldability.
The present inventor's group proposed, as a novel polycarbonate being excellent in flame retardance, mechanical strength and other properties, a polycarbonate which is obtained by using pentahalogenophenol as an end terminator, and by copolymerizing BPA and TBA (Japanese Patent Application Nos. 79227/1989 and 79228/1989). Said polycarbonate, however, was found to have a few problems in thermostability at molding, although it is excellent in flame retardance and mechanical strength.